1. Field of the Invention
The invention relates to an improved process latitude, especially depth-of-focus, projection mask for forming contact or via hole openings in a photoresist masking layer in the formation of semiconductor integrated circuits. The improved process latitude mask uses an opaque blocking area in the center of the primary opening in the projection mask. The area of the opaque blocking area is no larger than the area of the primary mask opening divided by nine and will not form a pattern in the photoresist. The opaque blocking area alters the light intensity at the photoresist and improves the process latitude.
2. Description of the Related Art
For high resolution applications the process latitude of conventional projection masks for forming contact or via hole openings in photoresist is limited and often will not be sufficient to accommodate the surface variations of the semiconductor wafer being manufactured. There have been attempts to improve process latitude with small enlargements at the corners of a square primary opening in a projection mask. This invention uses an opaque blocking area in the center of the primary opening of the projection mask.